From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:48925) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1WrTvS-00040Q-T5 for qemu-devel@nongnu.org; Mon, 02 Jun 2014 11:13:34 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1WrTvL-0005pk-ED for qemu-devel@nongnu.org; Mon, 02 Jun 2014 11:13:26 -0400 Received: from mx1.redhat.com ([209.132.183.28]:52832) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1WrTvL-0005pe-6J for qemu-devel@nongnu.org; Mon, 02 Jun 2014 11:13:19 -0400 Message-ID: <1401721991.22391.57.camel@nilsson.home.kraxel.org> From: Gerd Hoffmann Date: Mon, 02 Jun 2014 17:13:11 +0200 In-Reply-To: <538C7789.9000008@citrix.com> References: <20140602124506.GG28039@redhat.com> <538C7789.9000008@citrix.com> Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [Xen-devel] Xen hypervisor inside KVM guest with x2apic CPU feature fails to boot List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Andrew Cooper Cc: xen-devel@lists.xensource.com, qemu-devel@nongnu.org, kvm@vger.kernel.org Hi, > > (XEN) **************************************** > > (XEN) Panic on CPU 0: > > (XEN) IO-APIC + timer doesn't work! Boot with apic_verbosity=debug and send a report. Then try booting with the 'noapic' option > > (XEN) **************************************** > > Just tried the same a few days ago. Adding a second vcpu made things work. > I am going to go out on a limb and say it is unlikely for the Xen side > of things to be broken. We have machines in XenServers test lab which > support x2apic but have it disabled in this manor because of a lack of > EIM (or due to errata). I'm not so sure. non-SMP setup with x2apic is probably pretty rare on physical hardware and I wouldn't be surprised if that happens to hit a untested code path in Xen ... > I would look into what KVM/qemu does differently as a result of the > "+x2apic" flag, and whether it is simply the reported cpuid feature, or > whether it affects the legacy ioapic emulation. ... but enabling x2apic for a guest depending on legacy ioapic stuff is pretty unlikely too, so that setup being emulated incorrectly without being noticed so far wouldn't surprise me too. cheers, Gerd